There is information in the rotation curve beyond the TF relation.
The shapes of rotation curves are also related to luminosity, as noted by
Rubin et al. (1985)
and Persic & Salucci
(1991).
Though I would not
claim as strict a relation as implied by the ``universal rotation curve'' of
Persic & Salucci, a correlation does exist and provides an additional test
(Figure 2).

Figure 2. The systematic dependence of the
shape of rotation curves on
luminosity and disk scale length. R34 is the radius
at which V(R)
has reached 3/4 of the asymptotic flat velocity. A large
R34 corresponds
to a slowly rising rotation curve. R34 varies greatly
between galaxies of the same luminosity but different surface brightness
when R34 is measured in kpc. However, there is a good
correlation in this diagram when R34 is normalized by
the disk scale length h. Some, and perhaps most, of the
scatter is attributable to observational uncertainty. Also shown are
model predictions of
Dalcanton et
al. (1997),
with numbers labeling
points by the logarithm of the halo mass. The models track in the opposite
sense of the data, a problem generic to SH models which have not been tuned
to fit the data.

LSB galaxies adhere to the relation between luminosity and rotation curve
shape, provided that the radius is measured in units
of the disk scale length (see also Verheijen, these proceedings).
This implies that a good estimate of the rotation curve of any galaxy can
be made from measurements of only two photometric parameters
(L, h).
Even though the dynamics are dominated by dark matter, we need only know
the distribution of luminous matter to predict the rotation curve.

This strong coupling of mass and light (as long stressed by Sancisi)
is a general problem.
It always leads to fine-tuning paradoxes, with the tail wagging the dog.
The dominant, spherical halo composed of non-baryonic dark matter
simply should not be so intimately related to the details of the
luminous disk.